This invention relates to the interconnecting of electric power transmission lines when conductor bundles are insulatively attached to a dead end tower.
Overhead electric power transmission lines, such as high voltage lines, are connected to dead end towers for a variety of reasons. It may be where the line turns or where protection is required from domino-type failures or where the topography of the land beneath the lines dictates a more stable support to meet the physical line loadings involved. With the introduction of ultra high voltage (UHV) transmission lines in the 1,000 kilovolt (kV) range and higher, the conductors of these lines have been grouped into generally cylindrical bundles of 5 to 16 or more conductors with each conductor within a bundle commonly referred to as a line subconductor. This large number of heavy line subconductors--typically three or six bundles or phases for ac and two or four bundles or poles for dc--arriving at a dead end tower presents a multitude of mechanical and electrical problems in jumpering through or around the tower. These bundles of elongated concentrically arranged line subconductors can be collectively thought of as a single large expanded conductor where the electrostatic and electromagnetic fields are concentrated on the outside of the bundles with little or no fields interacting within the bundles. In the present invention, the internal jumper conductors, fittings, and jumper buses are all within this inherently electrostatically and electromagnetically shielded internal bundle region. This allows smaller diameter jumper conductors of standard lengths, regardless of terrain or line angle, to be used for the jumper conductors without causing any noise or corona, and they can be conveniently and efficiently shop fabricated. One further advantage of this internal jumpering, which allows the external jumpers to connect to a jumper bus, is the elimination of the problem in the prior art of getting the external jumper between the subconductors of the line bundle to connect directly to the fitting ends of the line subconductors without wear and damage over a period of time from rubbing against each other during their movement due to the elements.
In the past, when a bundle of line subconductors was to be connected at a dead end tower to the continuing segment of the line, the jumper bundle subconductors were directly connected to the line subconductors by bolting together the pads of their respective compression fittings as later shown in FIG. 4. In such an arrangement, a good proportion of these external jumper subconductors must go between or closely adjacent to the relatively closely spaced line subconductors to make this connection. This becomes impracticable as the number of line subconductors in a bundle is increased or as the overall diameter of the bundle is reduced or where asymmetric bundles are used wherein the spacing between subconductors is reduced in the bottom portion of the circular bundle to optimize the electrical design of the bundle. These external jumper subconductors must normally have the same diameter and number as the large line subconductors and also maintain their circular configuration because they are both exposed to the same high voltage gradient external to the bundle. It is extremely difficult to maintain the jumper bundle configuration or to make proper connections to the line subconductors with such large diameter, hard and stiff jumper subconductors. And even when such connections are made, the jumper subconductors and adjacent line subconductors are subject to mechanical damage under dynamic conditions caused by ice and wind. Thus, although external jumpering of an electric power transmission line conductor bundle is possible, it is impractical because of the multitude of limitations it presents.
Representative patents are the two U.S. Pat. Nos. to Otsuki, et al. (3,624,268) and Okada et al (3,647,933) and the Austrian Pat. No. to Hofmann (177823). Otsuki, et al. externally jumpers the transmission line subconductors to provide a rigid jumper cable capable of withstanding the swinging movements of a flexible jumper to insure electrical tower clearance. As the external jumpers are fully exposed to the external voltage gradient of the subconductor bundle, their jumper subconductors must be the same diameter as the line subconductors. Such is not the case with the present invention as all internal jumpers are inherently electrically shielded by virtue of being entirely internal to the transmission line bundle and thus may be of substantially smaller cross-sectional diameter than the line subconductors. The patent to Okada, et al. discloses a swayable supporting insulator beam attached to a dead end tower with its jumper being useable for either a single or twin bundle transmission line. Hofmann discloses a jumper fitting for attaching a single jumper to two or more jumpers that are externally connected to the subconductors of a transmission line bundle. Other patents of general interest are: Japanese Pat. No. (44-21073), Japanese Pat. No. (46-31428), Japanese Pat. No. (46-38231) and Barton U.S. Pat. No. (3,129,279).
Various other objects and advantages will appear from the following description of an embodiment of the invention, and the most novel features will be particularly pointed out hereinafter in connection with the appended claims. It will be understood that various changes in the details, materials, and arrangements of the parts which are herein described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention.